Slacker sets you free to listen to customized radio

— -- Have you taken note lately of all the ways to carry music in your pocket? The iPod lets you schlep boatloads of songs from your own collection. Zunes, Sansas and other gadgets let you listen to an unlimited number of "rented" tracks, provided you remain a paying customer. Portable satellite radios from Sirius and XM serve up numerous channels that cater to very specific musical tastes.

That wouldn't seem to leave much room for the new Slacker Portable I've been testing. But it adds an attractive if imperfect option.

The device finally started shipping the other day, not quite a year shy of when the free Slacker Personal Radio online service first launched.

Slacker on the Web lets you construct custom Internet radio stations you can listen to on a PC. You type a performer's name and then choose which related artists to add. You can fine-tune Slacker stations by having them play more familiar hits, or obscure ditties. In all, Slacker has more than 2 million songs (from major labels and independents) and over 10,000 artist stations.

The portable player lets you access those stations wherever you happen to be. A station's programming lineup of songs is refreshed whenever you tap into a Wi-Fi network or connect a USB cable.

But here's the delicious part. You need not be tethered to a computer or have access to Wi-Fi to listen, because songs are "cached," or stored in the device's memory. And that means you can use Slacker on the subway or an airplane.

Slacker fills a niche not directly addressed by rivals. For all the musical genre stations on XM or Sirius, for example — and I'm a big fan of both services — the satellite alternatives don't let you customize your own channels.

Slacker is free, unlike subscription music services such as Rhapsody.

The benefit against an iPod or other MP3 player is that your own collection of tunes might grow stale — and you don't always get around to loading new stuff.

And by connecting Slacker via USB cable to a PC, you can load your own tracks as with any standard digital player, provided they're in the MP3 or unprotected WMA formats. This option is not available for Macs.